You could get some heavy metal added to the balancer, but probably cheaper to buy a new gilmer gear with 4 holes. You could spin the gear you have in a lathe and scribe an arch, then redrill it to 4 hole, pretty easy to do. No trouble to balance a 28oz flywheel or flex plate to 50oz, just weld some weight to a flex plate and take weight away from the opersite side on the fly wheel, balancer is harder as I have said you would need to add mallory metal. Redrill the gilmer that's what i would do, or throw it away and put V belts on it, they are a waste of time anyway, just like gear drive cam gears. Also if the engine you have had a serp belt the water pump will likly turn the wrong way, and you'll cook it, you need to run the early water pump.